The intervertebral discs form cartilaginous joints between the end plates of vertebrae to provide shock absorption. The discs include two main regions: the nucleus pulposus, which is an inner, soft and highly hydrated structure, and the annulus fibrosus, which is a strong structure including lamellae (concentric sheets of collagen fibers), which surrounds the nucleus. The three major constituents of the discs are water, fibrillar collagens, and aggrecan. The proportion of these components varies across the disc, with the nucleus having a higher concentration of aggrecan and water and a lower collagen content than other regions of the disc. The loss of water content, particularly in the nucleus pulposus, is associated with disc degeneration, and with a decrease in disc height and abnormal loading of other spinal structures.
US Patent Application Publication 2005/0277996 to Podhajsky, which is incorporated herein by reference, describes a method for reducing intervertebral pressure, including providing an electrode, having proximal and distal ends, and a generator, which is operatively connected to the proximal end of the electrode, and is configured to supply radiofrequency current thereto. The method also includes inserting at least a portion of the distal end of the electrode into the nucleus pulposus of an intervertebral disc and activating the generator to heat the nucleus pulposus. The electrode may be inserted into the intervertebral disc through its first lateral side and/or its second lateral side, and may be substantially parallel to the major or minor axis of the nucleus pulposus.
U.S. Pat. No. 6,997,941 to Sharkey et al., which is incorporated herein by reference, describes a device that is positioned at a location in an intervertebral disc for diagnosis or treatment of the disc. Treatment may include, for example, applying energy or removing material, and may decrease intradisc pressure. Radiofrequency energy may be applied. A percutaneous method of repairing a fissure in the annulus pulposus comprises placing an energy source adjacent to the fissure and providing sufficient energy to the fissure to raise the temperature to at least about 45-70 degrees C., and for a sufficient time to cause the collagen to weld.
US Patent Application Publication 2003/0225331 to Diederich et al., which is incorporated herein by reference, describes an implantable ultrasound therapy system and method that provides directional, focused ultrasound to localized regions of tissue within body joints, such as spinal joints. An ultrasound emitter or transducer is delivered to a location within the body associated with the joint and heats the target region of tissue associated with the joint from the location. Such locations for ultrasound transducer placement may include, for example, in or around the intervertebral discs, or the bony structures such as vertebral bodies or posterior vertebral elements such as facet joints. Various modes of operation provide for selective, controlled heating at different temperature ranges to provide different intended results in the target tissue, which ranges are significantly affected by pre-stressed tissues such as in-vivo intervertebral discs.
US Patent Application Publication 2004/0116977 to Finch et al., which is incorporated herein by reference, describes a method for electrically stimulating an area in a spinal disc. The method comprises implanting a lead with one or more electrodes in a placement site in or adjacent to one or more discs at any spinal level from cervical through lumbar, connecting the lead to a signal generator, and generating electrical stimulation pulses using the generator to stimulate targeted portions of the disc. Additionally, a system for relieving pain associated with a spinal disc is described that comprises a lead with one or more electrodes, an introducer for introducing the lead to a placement site in or adjacent to the disc, a removable stylet for guiding the lead to the placement site in the disc, and a generator connected to the lead for generating electrical pulses to the lead for stimulating the disc.
US Patent Application Publication 2004/0019381 to Pflueger, which is incorporated herein by reference, describes spinal disc therapy systems including an element for implantation into an intervertebral disc annulus or intervertebral disc nucleus. The implant element includes a biochemically active agent that provides pain relief, inflammation relief, or other benefit. The implant element may include a mechanically active component that radiates wave energy, for example, in the form of electrical or magnetic energy.
US Patent Application Publication 2004/0049180 to Sharps et al., which is incorporated herein by reference, describes systems and methods for selectively applying electrical energy to a target location within a patient's body, particularly including tissue in the spine. High frequency (RF) electrical energy is applied to one or more electrode terminals in the presence of electrically conductive fluid or saline-rich tissue to contract collagen fibers within the tissue structures. In one aspect of the invention, a system and method is provided for contracting a portion of the nucleus pulposus of a vertebral disc by applying a high frequency voltage between an active electrode and a return electrode within the portion of the nucleus pulposus, where contraction of the portion of nucleus pulposus inhibits migration of the portion of nucleus pulposus through the fissure.
US Patent Application Publication 2004/0210209 to Yeung, which is incorporated herein by reference, describes methods for delivering and deploying conduits into an intervertebral disc to re-establish the exchange of nutrients and waste between the disc and bodily circulation, in order to stop or reverse disc degeneration and relieve pain. The intervertebral disc installed with semi-permeable conduits may be used as an immuno-isolated capsule to encapsulate donor cells capable of biosynthesizing therapeutic molecules. The semi-permeable conduits establish the exchange of nutrients and therapeutic molecules between disc and bodily circulation to treat a disease without using immuno-suppressive drugs.
The following references, all of which are incorporated herein by reference, may be of interest:    Vernengo J, “Injectable Bioadhesive Hydrogels for Nucleus Pulposus Replacement and Repair of the Damaged Intervertebral Disc: A Thesis,” Drexel University (January 2007)    Cheung K M C et al., “Intervertebral disc regeneration by use of autologous mesenchymal stem cells, an experimental model in rabbits,” Abstract from the SRS 2004 Annual Meeting    Freemont T J et al., “Degeneration of intervertebral discs: current understanding of cellular and molecular events, and implications for novel therapies,” Expert Reviews in Molecular Biology, Mar. 29, 2001 (Cambridge University Press)    Urban J P G et al., “The nucleus of the intervertebral disc from development to degeneration,” American Zoologist 40(1):53-61 (2000)    U.S. Pat. No. 6,161,047 to King    U.S. Pat. No. 4,044,774 to Corbin et al.    U.S. Pat. No. 6,146,380 to Racz et al.    U.S. Pat. No. 5,433,739 to Sluijter et al.    U.S. Pat. No. 5,121,754 to Mullett    U.S. Pat. No. 5,938,690 to Law et al.    U.S. Pat. No. 6,360,750 to Gerber et al.    US Patent Application Publication 2002/0151948 to King et al.